Boost converters are used as active power circuits, as part of an off AC line powered power system, for controlling the wave shape of its input current as it is received from AC line power source. Wave shape control is provided by an active power switch of the converter which allows the current waveform to be constrained to approximate the wave shape of the input AC voltage waveform. The active power switch and the boost diode of the boost converter experience significant losses due to the reverse recovery loss characteristics of these devices as they are turned off.
Reduction of these losses is presently achieved by means of an auxiliary circuit shunting the active power switch and possessing an auxiliary active switch that conducts the input current at turn-off of the boost diode. The success of this approach is dependent on limiting the amount of power that the auxiliary power switch must handle. This necessity to limit the power handled by the auxiliary power switch and the complexity of the auxiliary circuit limits the application of this approach at higher power levels in excess of 1 KW.
An alternative approach uses a snubber circuit to minimize switching losses in the active power switch. Such an approach as illustrated by the lossless snubber disclosed in U.S. Pat. No. 5,260,607 comprises two additional inductors, three additional high voltage diodes and a capacitor. While this particular arrangement does minimize switching losses on the converter, it does so at the expense of circulating a significant level of energy in the converter due in part to induced ringing across the active switch during its off period. This circulating energy causes considerable power dissipation in the converter since the reactive components are not ideal but do indeed dissipate real energy. A second snubber circuit is required to damp the induced ringing in any realization of a practical circuit.